Error control codes are commonly used in electronic systems to detect and/or correct data errors, such as transmission errors or storage errors. One common use of error control codes is to detect and correct errors with data stored in a memory of computer system. For example, error correction bits, also called check bits, can be generated for data prior to storing data to one or more memory devices. The check bits are appended to the data to provide a data structure that is stored in memory. When the data is read from the one or more memory devices, the check bits can be used to detect or correct errors within the data. Errors can be introduced, for example, either due to faulty components or noise in the computer system. Faulty components can include faulty memory devices or faulty data paths between the devices within the computer system, such as faulty pins.
Error management techniques have been developed to mitigate the effects associated with these errors. One simple technique used for personal computers is known as parity checking. Parity checking utilizes a single bit associated with a piece of data to determine whether there is a single bit error in the data. Parity checking cannot detect multiple bit errors and provides no means for correcting errors. A more sophisticated system, such as a server, uses error correction codes (ECCs) to detect and correct some errors. A typical ECC system may use eight ECC bits (check bits, correction bits) for a 64-bit piece of data. The ECC bits provide enough information for an ECC algorithm to detect and correct a single bit error, or to detect double bit errors.
One error correction feature employed by servers is referred to in the industry as chipkill. The term chipkill refers to the ability to correct multiple bit errors in memory, where multiple bit errors are confined within the width of the memory device. For example, for a 32Mbit dynamic random access memory (DRAM) device that is 4 bits wide, a system that supports a chipkill function would be able to correct a 4-bit wide error in the memory device. Thus, the failure of an entire 4-bit wide DRAM chip during a DRAM cycle (e.g., read operation, write operation) in a configuration that supports chipkill would not cause the system to fail. Chipkill allows a system to operate in the event of multiple bit errors in any one memory device.